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What prevents a passenger from opening the emergency door on his own will, mid-flight?
I have never sat on the emergency seats near the wings, with the emergency exit. I have seen cabin crew instruct the passengers seated near the door on how to operate the door.
My question, what prevents a 'rogue' passenger from opening them mid-flight?

The answer should start with "if a passenger wants to open a door mid-flight, and if we freeze time to stop the other passengers running in his direction to beat the s**t out of him, then ... pressure differential ... etc."

Well, it actually happen: http://skift.com/2015/05/12/chinas-growing-epidemic-of-passengers-opening-planes-emergency-exits/

@HorusKol I imagine this could happen just after take-off roll (not yet mid-flight, but already in the air)

At cruising altitude there is between 4 and 8 tons of pressure acting on the inside of the door. There aren't too many passengers capable of exerting that much force on the handle (and even fewer handles that won't just snap off). Latch type doors have interlocks or over-center latches that prevent operation with a pressurized cabin.
It's theoretically possible to open the over-wing exits at approach altitudes when there is no pressure differential. Other than being windy/noisy it would not affect the flight in any way. Cabin doors usually open forward, good luck pushing them open against the airflow. If the person who pulled the window plug wants out, it's their (and only their) funeral. I've sat in the open doors of light aircraft in flight hundreds of times, legs in the breeze, no seatbelt, while the plane makes fairly steep turns toward the open door side. It's not a problem.

I've done it too, usually just before jumping out :)

@rbp I usually had to ride the plane down to pick up the next load.

"Legs in the breeze" not on the rudder pedals?  Also every jump pilot I saw wore a chute.

@rbp a) never said I was flying it, b) never said I wasn't wearing one

I thought most plane doors open outwards. Given that the inside of the plane is pressurized (above ambient pressure), does that not mean that the pressure is acting to OPEN the door?

@Aron no. Just because the door swings outward doesn't mean it opens outward. https://www.youtube.com/watch?v=C9_BUR8rGtE Watch carefully - the door is released, moves IN, then rotates and swings out. Yes, the hinge mechanism is rather complex.

@paul probability less complex than a latch that needed to hold "several thousand feet of air" in.

You could also theoretically open the over-wing exits at cruise altitude / speeds if the aircraft lost cabin pressure for some reason. I would however respectfully suggest that in such a situation there are probably more immediate concerns than some crazy person opening the emergency door at altitude :)

@Aron no, a latch that holds in multiple tons is fairly simple. Heavy, but simple. Cargo doors open out because they want to load an extra container behind it, and they aren't concerned about the cargo trying to open it in flight.

@paul: Note that even a "fairly simple" latch doesn't always work.

In addition to the pressure differential, some aircraft also have mechanical locks. Here's the logic diagram for a 737 NG. This will be similar to all of Boeing's exit doors that are hinged at the top.

These conditions cause the emergency exit doors to lock:

Three or more of the entry/service doors are closed, and
Either left or right engine is running, and
Air ground logic is in the AIR MODE, or
The left and right thrust levers are advanced more than 53 degrees

Could you add some clarifying text for those of us that can't read a logic diagram and/or aren't familiar with the terms used?

So if 3 or more doors are entry/service doors are closed, no emergency door can open? So even on the ground with the engines off, if no one can open a non-emergency door for some reason, the emergency doors won't open either?

@Dronz No, the rightmost logic gate is an AND. If 3 or more entry/service doors are closed; AND at least one engine has N2 >=50%; AND BOTH thrust levers are advanced more than 53 degrees OR the air/ground logic is in "air mode", THEN the doors lock. If at most 2 entry/service doors are closed, OR both engines are under 50% N2, OR at least one thrust lever has been advanced less than 53 degrees AND the air/ground logic is in "ground" mode, then the doors are not locked.

Hmm really interesting. Shows how far the aircraft engineers go to take care of security.

Could you indicate the source from which you took this diagram?

@cpast Does airbus/A320 also have the same logic?

A320 family have plug type overwing exits and so don't need this mechanical lock.

At $10,680 m$ cruising altitude air pressure is $23.8 kPa$ / $3.45psi$ / $23,800 N/m²$; compared to $101kPa$ / $14.7psi$ / $101,000 N/m^2$ at sea level.
Now a 747 for example has a pressurization altitude of $2,440m$ which equates to an internal pressure of $75kPa$ / $10.9psi$ and a force of $75,000 N/m^2$.
So the internal pressure of $75,000 N/m^2 - 23,800 N/m^2 = 51,200 N/m^2$
Door dimensions are $1.93m (H) \times 1.07m (W) = 2.07m^2$
Or in feet & inches: $6'4" (H) \times 3'6" (W) = 22.17 sqft$
So $51,200 N/m^2 \times 2.0651m^2 = 105,733.12 N$
Which equates to roughly 11.88 Metric Tonnes of force on the inside of the door! The door being larger than outside portal of the door. It is forced into the frame with considerable pressure.  It would be impossible for a human to operate the door under that force.

Depends on their tools--you could develop that force with a block and tackle.  (That doesn't mean you'll get it open, though--I'm sure you'll just bust the handle instead.)

The pressure differential will stop you.
In flight the airplane is pressurized to keep you conscious at high altitude. The doors plug doors with flanges and must be pulled inwards to open them; those flanges make them impossible to move even after you release the latches.

But pressurization in the cabin will create a grater pressure inside the plane and with a smaller pressure outside the door should be pushed out ...

@Davide check my edit

Oh right I did not know about that system !

What about when the aircraft is not pressurized (beginning of climb and approach)?

A young man jumped from a plane :
The Globe and Mail
"The Beechcraft King Air 200 turpoprop aircraft was flying at about 23,000 feet at the time of the incident."

I wonder if this could have something to do with it being a turboprop or lower altitude?

Or a different style of door. Without looking, I would suspect that a King Air 200 has slightly different certification requirements than a Part 121 transport.

For those truly interested Google 14 CFR 25.783 Fuselage Doors for Transport Category aircraft and 14 CFR 23.783 Doors for Normal Category aircraft which is what the King Air is.


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Are there procedures to follow in case of a suspect Electronic Control override (hacking)?
I am a filmmaker who made a film most pilots have seen (405) http://youtu.be/Tpx6o4gvmXE
I am working a new production that also takes place aboard an airliner. In it a telekinetic little girl is overriding the flight controls. But it is thought to be some sort of electronic control interference for a short time. Are there procedures a flight crew would follow in the initial stages if their controls seemed "possessed?"

Related to http://aviation.stackexchange.com/questions/2292/can-a-boeing-777-be-hacked TL;DR hacking an airplane in real life is not realistic... but neither is an airplane landing on a Jeep. Pilots don't have a "If instruments are possessed" checklist, but individual instruments giving erroneous readings is something every instrument pilot trains for. It is mostly a matter of cross-checking. Some things can be shutdown (by pulling the fuse/breaker) if it is detected to be faulty.

I think if you listed a few instruments you were particularly interested in and asked what the procedures are if they were to become faulty, that might help generate some higher quality answers.

Don't know if this is an good answer for you.
But this topic became well spoken during the disappearing of flight MH370. External Link of Remote Control System Edit: Seems @Bret Copeland already commented this perspective of the topic.

controls and instrumentation do not "seem possessed": either they are working or not.

Good notes. It's a supernatural thriller, so in some ways the instruments are possessed. What we have is the flight crew fighting with the plane as something tries to turn it around. Physically fighting with the controls.
https://vimeo.com/108521192

@BruceBranit: Yes, physically fighting the controls is what they'd do. They wouldn't really have time to think why.

You know, it might be a bit more interesting if the girl decided to make the instruments lie to the pilots.  Pilots rely very very heavily on instruments to guide them, and if they don't know they are faulty, would follow them in IFR conditions.  If the GPS started lying, or the VOR started lying or the artificial horizon started lying...and they followed it...that could be an interesting story.  Especially since eventually, one would suppose, they would start to suspect that something is wrong with the instruments (at which point they can start trouble shooting.)  Just my two cents.

For a real-world example of a lying VOR in action, see this AvHerald link.

@jaycarr, navigation-wise, wasn't this the main plot point of tomorrow never dies?

There are procedures for when some instrument indicates false values for how to find which one is not to be trusted and what to do if particular instrument cannot be trusted.
But for primary flight controls, not really. If the aircraft is flying on autopilot and initiates unexpected manoeuvre, the pilot will hit the autopilot disconnect button and take over manually. But beyond that, the pilot will just try more pressure on the controls to get the plane where he needs to. And won't really have much time to think about the reason.
You may want to look at the incidents and accidents caused by B737 rudder reversal. The rudder suddenly deflected in opposite direction than commanded and the pilots were not really able to understand what is happening in the short time they had to react. Somewhat similar incidents where the rudder failures of B747 (Northwest 85, here is captains account of the incident; there was one other similar occurrence). Again, the pilots just fought the controls; finding out what happened was not really possible and wouldn't help much anyway.
So I'd say there is really no time to "think it to be some sort of electronic control interference". The pilots would simply disconnect autopilot (if it didn't disconnect already due to pressure on controls) and then they would fight the controls.
Note that in all aircraft except Airbus A320 and newer and Boeing 777 and 787 the control column is mechanically (cables in smaller aircraft, hydraulically with some kind of power amplification on larger ones) connected to the control surfaces. So the pilots would be directly fighting the telekinetic power with their muscles. On Boeing 777 and 787 there is electronic intermediary, but the link is still bidirectional and control column position still corresponds to control surface position.
Only Airbus A320 and newer has the side-stick connected to a computer that calculates the final command from the pilot input and inertial reference. In this case the telekinet would either try to move the surfaces, but then would be fighting the computer, which has all power of the hydraulic system to it's disposal, or would try to move the side-stick under pilot's hand, but then the other pilot could press control priority button to take over. Of course even on Airbus the pilots can pull the circuit breaker and disable the computer, but then they are left with trim wheels and rudder pedals that both do have direct hydraulic links.

I think there are a variety of ways to do what you want.

You can have the girl take over the autopilot, rather than the controls, and prevent the pilot from disconnecting the autopilot.
Or you can have her physically take over the controls themselves (telekinesis), and the autopilot will automatically disconnect when pressure is applied to the controls
Or you can have it be a fly-by-wire aircraft (hello Airbus), and have the girl take over the fly-by-wire system, bypassing both the autopilot and the controls, and taking control of the control surfaces herself

you'll also have to figure out what you want to do regarding the throttles. Most passenger jets have autothrottles, but if someone is flying the plane by hand, and there is a change in altitude, then the throttles may need to be adjusted.
Some of this is going to depend on whether the girl has power over physical objects, or the ability to control electronic energy, or both
IIRC, there is an episode of Firefly where River takes over the ship using her telepathic powers. Might be worth consulting.

Love the Firefly reference. I worked on VFX for that show.

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How can hang gliders and paraglider pilots prevent stall?
Aircraft and gliders usually have instruments to measure air speed and angle of attack, which should be monitored to prevent stalling the aircraft.
However, it seems that most paragliders and hang-gliders lack such kind of tools.
How do the pilots avoid stalling without these kinds of instruments?

FWIW, in a light plane you don't usually detect stall or near stall conditions with instruments, you feel it.  Though there is a stall warning in some (if not all) planes, the only times I've ever heard it go off was when practicing stalls in training.

Paraglider Pilots can induce a stall by holding the brakes at seat or waist height until the wing retards. The wing does not want to do this and will resist but a full stall will eventually be induced this way. Pilots will feel and hear the reduction in forward airspeed. To come out of a stall, the pilot may smoothly move the position of the brakes upwards anticipating a surge where the wing recovers and may dive or surge in front of the pilot. Performing a 360 in light wind conditions, the side of the wing on the inside of the turn may stall. Typically, smoothly and promptly coming out of the turn using the brakes, will cause the wing to recover, failure to recover may result in a flat spin. Flying near full speed with minimum brake also risks a deflation of the wing on the left centre or right sides. This might be exacerbated if the pilots all-up weight is at the upper or lower weight limit of the glider; typically gliders come in xs s m l xl sizes. Prompt appropriate use of the brakes is pretty much all a paraglider pilot has to recover normal flight in all the scenarios above. If in doubt pilots should follow the instructions in the gliders manual and ensure they have enough recent flying hours in the conditions they wish to fly that they can do so safely, ie not freeze, recognise the symptoms of a stall for their glider, and react appropriately. Like all aircraft it won't be possible to recover from a stall below a certain height, so a pilot should have enough skill not put themselves at risk whilst still having fun!
I imagine hang glider pilots will feel and hear the wind, and be aware of the pressure on the control bar. I'm guessing their priority will also be to get air flowing over the wing by pulling in on the control bar - but I'm only guessing as I was a PG pilot not an HG pilot.

So the answer to the main question is "experience"?

Your answer is very informative. However it focus on how to create a stall instead of how to predict it. Do you mean that it cannot stall without pilot action ? To predict it a pilot must then "feel" the air to anticipate a stall ?

Yes it's done by feel. If you were in a regular aircraft with no ASI and no AoA indicator how would you do it? You'd know you were about to stall because you'd hear less wind noise as air speed bleeds away and maybe a pitch up attitude. If a PG pilot applies brake they're going to increase the AoA which will reduce speed and increase lift. It takes physical effort to keep the brakes held down, just before stall the brakes will feel soft moments before the wing stops flying. The pilot must slowly let up on the brakes to get out of the stall. Again, all this is done by feel.

@Notts90 yes I guess so. I was taught to "feel for the stall" when learning. Pilots can attend Special courses, usually over water, where they are taught to put the glider into stalled position and then follow procedure to get back to normal flight - or crash land into water if they don't recover quickly enough!

Paraglider pilots learn "active flying", whereby you use feedback from the wing to determine what's going on. You monitor the tension in both controls (the "brakes"), and the wing's attitude (if the wing pitches forwards then you feel like you are swinging backwards).
In bumpy air (such as on the edges of thermals, or in wave) active flying is used to keep the wing more or less above your head. If the wing surges forwards then you risk a collapse; if the wing falls back then you risk a stall.
In smooth air a stall is only likely if you are pulling the brakes down too far. This can happen accidentally, especially in nil-wind landings if you mistake your ground speed for airspeed.

Nice answer, and welcome to aviation.se!

+1 for mentioning the collapse.  Paraglider wings are unlike fixed-wing aircraft because they need air inflating them to maintain the aerofoil shape, mess up the airflow and you can lose the shape.  Personally, I know that if the wind on my face is too fast or too slow I know I'm in trouble

Well in case of hang gliders there is notable amount of force on speedbar (control handle) which always tries (in case of properly designed glider) to move speedbar back to trim speed position which is near stall + 10kph. Also, due to combination of swept wing and washout (root has higher AoA than wing tips) stall starts from the root of the wing and causes slight nose drop. If pilot won't resist to it wing will restore its speed and full stall will be prevented. Full stall usually requires pilots intended actions and is performed only during landing flare. In rare cases full stall may happen in-flight as well, but it is result of poor decisions or aerobatics which is prohibited on HG. In most cases full stall is ended up with tumble and throwing of reserve chute -

Hang gliders are trimmed (hang point is such) that if you touch nothing you are above the stall speed.
During normal flight you never push out the control bar, you pull to speed up, and you release to trim to use that speed.
you only push past trim on the landing.
Also, they are built in such a way that the center of the wing stalls first (before the sides) and since that is the forward most point of the wing, a stall there will drop your nose. (while the rest of the wing is not stalled.)
if you get close to stall speed, the glider is less responsive "mushy".

Not a bad answer but you might consider addressing the case of a steep thermalling turn.  We do often push out (forward) quite a bit in such a case, to counteract the nose-down pitching effect created by the curvature in the airflow/ relative wind due to the circular flight path.  In other words the angle-of-attack associated with no push or pull gets shifted to a much lower aoa in a steep turn.  But that just makes it harder to stall; the bar would have to be ridiculously far forward to stall in a really steep turn, maybe longer than our arms can reach.

So first sentence of answer is still true even in very steep turn, second sentence arguably not.  Change to "During normal wings-level flight" and then it's true.

This doesn't add anything to PM.'s answer from 3 years ago. Care to add some details that were left out of that one to add value?

@FreeMan You are absolutely right . I had skimmed the first answers but missed that. (though I would say it is typically less than 10+stall) :-)

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Can aircraft other than rockets go to space?
I always wondered if it was possible for planes and other aircraft to leave the Earth's atmosphere. Normal commercial transport airplanes can fly pretty high, but then they need air to get the speed boost from. Reactive engines seem like a better idea, but I don't know how much importance air has for them.
Is it possible to get to space from Earth's surface using a non-rocket aircraft?

I guess that aircraft as the name implies uses air to gain and maintain altitude. Lift is a force created by an airfoil in the air. As soon as you remove air (definition of space), you also remove lift possibility, and the object becomes a spacecraft. So an aircraft cannot go to space only using its own capabilities.

Depends on what you mean.
Get to high altitude? Yes you can. It is really inefficient to get there, but some aircraft already do it.
Achieve a stable orbit and be able to maintain control? No, at those altitudes you do not have enough oxygen to keep your engines running, you have to bring your own (and thus use a rocket)

For the sake of clarity, some definitions:

reaction engine: includes both rockets and jets. The engine pushes some mass in one direction and by reaction it achieves thrust in the opposite one.
jet (engine): is used to refer to airbreathing engines. The aircraft carries the fuel, but not the oxidizer; that is taken from the surrounding atmosphere.
rocket (engine): is used to refer to non-airbreathing engines. The (space)craft carries both the fuel and the oxidizer. No atmosphere is needed.
space: above 100km of altitude.
go to space:

staying in space:

Images from xkcd

High altitudes aren't necessarily inefficient. Some amazing aircraft like the Lockheed U2 were very, very efficient at FL 700. Of course, the turbofans on the U2 can't get it too much further AMSL though.

@shortstheory U2 is efficient AT FL700, absolutely inefficient at getting there.

Can a spacecraft be merely "shot" into space, such as on an incredibility powerful railgun? I suspect the air friction would absorb all the energy too quickly. And the acceleration might be less than pleasant for the astronaughts xD

@Alexander Why don't we use catapults to get to space? on [space.se] probably covers much of that. Full disclosure: Accepted answer is my own.

@Alexander-ReinstateMonica   Yes, and theoretically you could achieve the same with a relatively standard jet-powered aeroplane - accelerate fast enough while within the atmosphere and momentum will carry you out. In reality the speed required is too high for current engine technology.

For certain values of "go to space", yes.  The Karman line (the altitude at which an airplane cannot generate enough lift to stay aloft at any speed slower than orbital velocity) is usually considered the lower edge of outer space.  This implies that with a powerful engine and enough fuel it's possible to "fly" up into space: you just keep gaining altitude and speed until you find yourself in orbit.
No aircraft has actually done this.  The X-15 and SpaceShipOne were both able to reach that altitude in zoom climbs; neither went fast enough to stay there.

to stay in orbit you need to achieve escape velocity, that is much harder then just getting up there for a bit

No, to stay in orbit you need to reach orbital velocity, which is much slower than escape velocity.  Fascinatingly enough, as I mentioned in my answer, the stall speed for an airplane flying at the altitude of the Karman line is orbital velocity.

I thought you had to do a particular maneuver to circularize your orbit though?  And that maneuver has to be done when you are outside of the atmosphere.  If you were to do it inside the atmosphere your orbital trajectory would take you back into the atmo and you'd decelerate, taking you out of orbit...  I suppose I'm splitting hairs, but it seems that a true orbit requires you to be outside the atmosphere, thus requires a rocket engine.

Granted, the question wasn't actually about getting into orbit, just about getting into space.  So the answer still works.

@JayCarr, to get a stable orbit, you need to raise both perigee and apogee to be outside the atmosphere.  To do this, you need to accelerate at both the high point and the low point of the orbit.  A conventional rocket needs to fire the engines twice to do this because the engines run for such a short period, but a "space plane" might not need to if it climbs into orbit gradually enough.

@Mark You'd still have to level off at the apogee though, which must be outside of the atmo if you don't want to risk de-orbiting, so you'd still need a rocket engine.  Really my point is if you want a stable orbit outside of the atmosphere, you will eventually need a rocket engine, because you will have to do some sort of maneuver in a vacuum.  Though, mea culpa, all my knowledge of this comes from hours of playing Kerbal Space Program, reality may differ ;).

@JayCarr, in the real world, "stable" is relative.  At 100km, you might manage to orbit once before re-entry; 300km will get you a few months, and 35,786km (geostationary orbit) has a decay time of millions of years.

@Mark - Ah!  So it sounds like your plan will work so long as stable orbit is defined as getting around a few times but no more?  Mkay, that makes some more sense now.

@JayCarr obligatory xkcd:  https://xkcd.com/1356/

X-15 and SpaceShipOne (and Two) are both winged, but they are still rocket-powered.

It depends what you include in "non-rocket aircraft".  Wikipedia has a whole article on "Non-rocket spacelaunch" which discusses the various options.
The short version is, there are no current space launch systems which do not use rockets.  The most practical one we know of appears to be space guns, which have been successfully used for sub-orbital launches (but are not practical for human spaceflight).

A jet engine can only accept air at around half the speed of sound. If the plane is flying faster, the inlet system needs to slow the air down before accelerating it again. Hence the higher the speed, the less thrust it can provide. It is not like a rocket engine that always pulls with comparable force.
A plane needs to accelerate to Mach 25 or about to fly into orbit as a spacecraft, and this is only possible with a new type of engine.
Scramjet that is a jet engine, not a rocket, could probably do this. However this engine seems still under development and currently a rocket is required to accelerate to the speed under that this engine can even be started.

I recall hearing about F-15s making ballistic suborbital flights, by simply getting up enough of a head of steam to coast through near-space. I don't think they actually went into "space" (100 km altitude) and they certainly didn't make orbit. Does anyone else recall the specifics on this? I can find some references online to using F-15s to test launch ASAT missiles, but my recollection was that the whole aircraft actually went high enough to get well above maximum cruising altitude.

It's called a zoom climb, and it's a fairly routine maneuver for getting an airplane above its maximum cruising altitude.

You might be thinking about the X-15, which was a rocket plane designed to be capable of suborbital flight.

X-15 is a rocket, no much less than Space Shuttle during the launch.

No aircraft powered by engines which rely on atmospheric oxygen can operate outside of Earths atmosphere, 100,000 ft is approximately the altitude limit for air breathing aircraft using conventional fuels, higher sustained altitudes might be possible using liquid hydrogen, but the utility of very high speed and altitude performance as a means of avoiding interception is questionable today. No air breathing aircraft is likely to outrun a rocket propelled Surface to Air Missile however apparently impressive it's performance statistics.

Related to the discussion in the last sentence, Could a SR-71 be shot down today?

Yes, in theory quite easily using the Surface to Air Missile systems currently in use by the United States and Russia, using as a basis the known target speed, maneuvering and altitude capabilities of these systems. As an example of the kind of dynamic performance obtainable from a missile, the Sprint missile developed for the Safeguard ABM system accelerated at 100 g to reach Mach 10 five seconds after launch, although this was a short range system. In principle though it should always be possible to design a missile system capable of downing any possible air breathing aircraft.

Lockheed Martin are promoting the SR72 on the basis that it will achieve Mach 6 at 80,000 ft, so we can assume that somebody somewhere thinks that this will make it difficult to shoot down.

I'm not sure how you'd classify the proposed Skylon spacecraft spacecraft. It would be an airbreathing reactive engine in lower altitudes but a rocket above 26 km.
It might be a game changer. But this time I don't give even odds that Skylon will come to pass.


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How does the canard plan of the Dassault Rafale work?
I'm quite puzzled after seeing some videos of the Dassault Rafale. When pulling the stick, the canard plan should move as in this video (low speed, high angle of attack, stick pulled backward on average). But, this a high load and high speed maneuver, the canard plan's position should be similar but it is not.
How is that possible? Does the canard plan act as a canard plan only at low speed, the elevon doing most of the job at high speed?
I'm double puzzled as this canard behaviour seems to be the same for the SU-30.

The answer is in two parts. First, at higher speeds, control surfaces have more air moving over them and so they don't have to angle as much to provide the same force necessary to move the jet as they do at slower speeds. In fact, a thin control surface like this canard will stall at lower angles of attack than a thicker profile would (the thinner profile reduces drag which is why it's used here), and a stalled surface can't do its job.
Second, modern jets like the Rafale have fly-by-wire systems with flight limiters, to avoid the pilot overstressing the airframe at high speeds. The first video shows the Rafale in landing configuration, approaching a carrier at maybe 150kts. The second video shows high-G maneuvers at probably between 300 and 400kts. The forces at play on the canard are, in general, related to the square of the speed of the air moving past them, so if the system allowed the canards to present the same angle to a 300-knot flow as a 150-knot flow, all other things being equal the canard would be under 4 times the stress. At 450 knots that canard would be under 9 times the stress. Very quickly you would exceed the mechanical strength of that canard surface entirely, and then you wouldn't have a canard surface at all. So instead, the canards are moved at a shallower angle, with the difference in pitch rate, up to what the flight limiter will allow the entire aircraft to do, is made up using the elevons on the wings.


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Why is the Tu-144 the only commercial airplane with canard configuration?
I understand the delta wing was chosen because of the supersonic cruise (like the Concorde), and canards were added to reduce the approach/landing speed. But canards may be used without delta wing (e.g. Focke Wulf F-19, Soukhoï Su-47, Rutan Voyager,...), so I don't understand why the canard wing configuration is not used among commercial aircraft.

Would it be helpful to add an image of the mentioned aircraft?

The FW-19 "Ente" was designed exactly for the purpose of testing wether a canard is the better choice for a commercial transport airplane. As it turned out, it wasn't. That settled the discussion and newer designs merely confirmed what had been found out back then.

Short answer: Canards make most sense with negative static stability and high maneuverability. Commercial aircraft don't need either, so a conventional layout works best.
For a statically stable aircraft, the conventional layout gives most efficiency with sufficient damping. Static stability requires that the forward lifting surfaces create more lift proportionally to their size than the rear surfaces. Here is an answer to a related question.
You want the airplane to return to the original flight attitude if it has been disturbed, say by a gust or a jolt on the stick. This can be done by creating proportionally more lift with the forward surfaces (= the wing in a conventional configuration) than with the rear surfaces (= the wing in a canard configuration). Say the jolt pitches the aircraft up. Now the aerodynamic forces should change in a way which increases lift proportionally more on the rear surfaces, so the aircraft pitches down and returns to it's original attitude. By distributing lift the way I mentioned above, the same change in angle of attack on both forward and rear surface will create a proportionally higher lift increase on the rear surface, making the aircraft (statically) stable.
That requires that one of the (mostly) two surfaces is not contributing as much to lift creation than it could. You want this surface to be the smaller one of both, so the whole configuration can create as much lift as possible at a given speed. A canard would be a poor choice for a commercial airplane, because the big wing would now fly at a fraction of it's potential.
Once you shift the center of gravity back to improve maneuverability, things get different: Now the rear surface is creating proportionally more lift, so the smaller surface should go in front. Voilá, a canard!
Now add forward sweep, which will make the wing tips twist to higher angles of attack when lift is increased, and you get a really responsive aircraft (but need to be careful not to overstress it!). This was done on the X-29 and the Berkut.
As jwenting pointed out, the canard on the Tu-144 was not a control surface, but should be considered a detached slat of sorts. Also, by adding some lift ahead of the wing it allows to lower the wing flaps in slow flight, increasing the lift potential of the main wing while maintaining the location of the center of gravity and stability.
And while we are at it: The Piaggio Avanti has a canard, and a conventional tail, too. Here the canard helps to put the wing spar behind the cabin area, makes it easier to fly with a wide range of c.g. locations and to increase aerodynamic damping. This is one of very few examples in commercial aircraft of canards done right!

You state that the conventional layout is the most efficient for a statically stable aircraft. So I guess this begs the question of why commercial aircraft continue to require static stability: is anything else considered too unsafe, even for cargo airplanes, and even if there are significant efficiency gains? I feel that is a major part of the original question.

@romkyns: Stricly speaking, natural static stability is not necessary if the FCS works. Also, an aircraft is still flyable with reduced stability, and if an unlikely failure means a limited workload increase for the pilot, reduced but still positive stability would be in line with current certification standards. But even then the canard would still be worse than a standard configuration. And consider this: I spoke around 1990 with A-310 pilots who flatly refused to ever fill up the tank in the empennage, because they wrongly believed this would make the plane instantly unstable.

The canards on the Tu-144 weren't canards technically. They were static surfaces, not moving.
They were purely lift devices to improve low speed handling (and thus help reduce landing speed which was excessively high).
These were added because low speed handling was found to be deficient, due to the inferior (as compared to Concorde) wing design.

A static canard is still a canard.

@slebetman jwenting's avatar leads me to think that he know about canard tho...

It wasn't the wing that was the problem (if anything, it was probably superior to Concorde's aerodynamically, and in any case had significantly lesser loading); rather, it was a combination of design decisions with closely packed engines and shorter landing gear. This made Tu more susceptible to tail strikes and greatly limited its landing attitude. Thus folding canards were added so that flaps could be used.

@Zeus the wing was a problem for low speed flight. At high speeds it was indeed very good. The factors you mention of course didn't help.

@Antzi I don't know what jwenting's avatar at the time of posting was, but the current avatar might lead one to believe there is extra insight into mallards, not canards.

@T.J.L. a canard is a French mallard. My knowledge of French is fairly limited, but I do manage not to starve when presented with a restaurant menu :)

Wordplay effective in two languages? I approve! :)

Because it is not aerodynamically efficient. To achieve stability the forward surface has to fly at higher angle of attack than the rear. So the canard has to fly at rather high angle of attack which leads to high drag and disrupts airflow for the main wing further reducing it's efficiency. It is not a chance that most modern jets have the same layout. It is most efficient known design.
Also while the higher angle of attack of the canard leads to it's biggest advantage, the gentle stall behaviour where the aircraft just gently lowers nose it means that the maximum usable angle of attack is reduced. This increases landing speed and reduces the safety margin should the aircraft get caught in a wind-shear. Suitable wing twist provides not much worse stall behaviour without these disadvantages.
With delta wings, the canard has advantage that it increases stall angle of attack and thus maximum lift, because the canard acts as vortex generator. This means sharper turns at high speed and lower landing speed, which is why this configuration is popular in fighters (Eurofighter Typhoon, Dassault Rafale, Saab JAS-39 Grippen) where manoeuvrability is more important than efficiency. Besides these designs are not stable (stabilized by computer instead; allows faster control response), so the canard does not produce that much drag.
The Sukhoi Su-47 uses canard primarily for layout reasons as the forward-swept wing does not leave much room at the tail, but a lot of room at the nose. And it's not clear how good the layout actually is; it does not seem to be followed by other military designs. Grumman X-29 first flew in 1984, but no follow up design was created.
The Rutan Voyager counters the inefficiency by not flying the canard at high angle of attack, which yields good efficiency, but poor pitch stability. It was manageable for good test pilots, but not suitable for average airline pilot. And note that this also eliminates the stall behaviour advantage of canard.

OK for the test pilots skill superiority, but nowaday almost all new commercial aircraft are fly-by-wire with computer stability enhancement.

@ManuH: The fly-by-wire actually reduces stability if it does anything to it. Airbus FBW makes the aircraft artificially neutrally stable, but aerodynamically the aircraft are still positively stable so it can be flown with the mechanical backup. And Airbus is alone (Sukhoi copies it in Su-100, but that's the only I know of); Boeing FBW only provides flight envelope protection, but leaves stability unaffected.

@ManuH: Of course military aircraft are a different matter. New fighters are almost always aerodynamically unstable and their FBW enhances stability (added complication is that supersonic aircraft are more stable in supersonic regime, so if they want to be highly manoeuvrable at supersonic speed, they end up unstable at subsonic). But it's not the case of any transport aircraft.

@ManuH, you're covering a lot of ground in a few words:
"...nowaday almost all new commercial aircraft are fly-by-wire with computer stability enhancement."
"The fly-by-wire actually reduces stability if it does anything to it."
"Boeing FBW only provides flight envelope protection, but leaves stability unaffected."
Slow down, indicate precisely what you mean to say.


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Is there any "instrument take-off system"?
Flying close to the ground is really dangerous and yet needed to land and take off. ILS is designed to keep the adequate trajectory close to the ground with (almost) no visibility. Is there a similar system for take off, e.i. a system helping pilots to maintain the adequate trajectory near the ground with almost no visibility at take off?

Yes, SIDs

SIDs should be compared to STARs. There is nothing compared to ILS for takeoff.

The closest thing to an instrument take-off system is a "takeoff guidance system", now simply referred to as a HUD by the FAA.  For more information on how that works, see this question.

While there is not a specific physical system dedicated to instrument departures per se, there are procedures that rely upon instrument flight rules (IFR) navigation equipment that ensure obstacle clearance when departing from an airport in instrument meteorological conditions (IMC).
From the Aeronautical Information Manual 5-2-8.

Instrument departure procedures are preplanned instrument
  flight rule (IFR) procedures which provide
  obstruction clearance from the terminal area to the
  appropriate en route structure. There are two types of
  DPs, Obstacle Departure Procedures (ODPs), printed
  either textually or graphically, and Standard Instrument
  Departures (SIDs), always printed graphically.
  All DPs, either textual or graphic may be designed using
  either conventional or RNAV criteria. RNAV
  procedures will have RNAV printed in the title,
  e.g., SHEAD TWO DEPARTURE (RNAV). ODPs
  provide obstruction clearance via the least onerous
  route from the terminal area to the appropriate en
  route structure. ODPs are recommended for obstruction
  clearance and may be flown without ATC
  clearance unless an alternate departure procedure
  (SID or radar vector) has been specifically assigned
  by ATC. Graphic ODPs will have (OBSTACLE)
  printed in the procedure title, e.g., GEYSR THREE DEPARTURE (OBSTACLE), or, CROWN ONE
  DEPARTURE (RNAV) (OBSTACLE). Standard Instrument
  Departures are air traffic control (ATC)
  procedures printed for pilot/controller use in graphic
  form to provide obstruction clearance and a transition
  from the terminal area to the appropriate en route
  structure. SIDs are primarily designed for system enhancement
  and to reduce pilot/controller workload.
  ATC clearance must be received prior to flying a SID.
  All DPs provide the pilot with a way to depart the airport
  and transition to the en route structure safely.
  Pilots operating under 14 CFR Part 91 are strongly
  encouraged to file and fly a DP at night, during marginal
  Visual Meteorological Conditions (VMC) and
  Instrument Meteorological Conditions (IMC), when
  one is available. The following paragraphs will provide
  an overview of the DP program, why DPs are
  developed, what criteria are used, where to find them,
  how they are to be flown, and finally pilot and ATC
  responsibilities.

There are many details involved in actually using these procedures to make safe departures in IMC. The Instrument Procedures Handbook Chapter 1 is an excellent resource for pilots who want to review these procedures, what they provide and how to use them correctly.
Here is an example of an ODP from my home airport, KCRG. There are some very tall towers less than 10 nautical miles from the airport. They are enormous and easy to avoid under visual conditions, but when IMC prevails these procedures are absolutely life-saving with such large obstructions nearby. They are taken from this takeoff minimums document.

Here is an example of a SID. These are always graphically depicted and will usually be found at larger airports. Here are pages 1 and 2 of the full SID.

As Simon mentions, there are the Standard Instrument Departure procedures. They need not be that precise. Remember that in landing, 50 ft verctial or in lateral (left/right) deviation can easily lead to a disaster. This is not true for departure once you are airborne; 50 ft make no difference, the separation of the used routes is much much larger. Before you are airborne, you see the runway below you, and you just double-check it's the correct runway and you've got enough length of it; but neither of these directly depends on the visual.
Last but not least, if the runway has an ILS in your direction or the opposite one, you can use its horizontal part to navigate yourself straight out of the airport; you can't use the vertical part of course, since the desired climb angle rarely coincides with the glide slope.

Using the localizer for runway alignment, as in a low-visibility takeoff using a HUD, you actually use the LOC for the runway you're using, rather than the opposite direction. Typically, only 1 or the other is turned on at a time.

Well, 50 (especially altitude) can make a difference on departure if your roll used most of the runway and there are obstacles that you need to climb over past the end of the runway. It doesn't make so much difference once you're above ground obstacles, though.


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What is different between HIR (Hold Items Record) and DIR (Deferred Items Record)?
I wonder what is exactly different between HIR and DIR?
What is different between HIR (Hold Items Record) and DIR (Deferred Items Record)?

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What is the pattern of the flashing light in Airbus A340-300?
I'm looking for the lights and flashing patterns of the Airbus A340-313 (or any Airbus A340).
My question is related to this one: Do lights on aircraft flash in a specific pattern?
but is very specific for this model.
In any case I'll be grateful is there is some page or link with the patterns of several models (so I don't have to disturb you in the future :) )
Thanks in advance.

From this discussion on Airliners.net: "Airbus does have a synchronization between the strobe and the beacon lights. heres an example if what it looks like. 1=1st wing strobe - 2=2nd wing strobe - 3=beacon. 1.2..3..1.2..3..1.2..3..1.2..3 so on and so forth"

Thanks mins! Also from that page is very interesting this part: Airbus uses a direction identification logic in their strobe lights. Forward facing strobes (left and right wingtip) double flash, whereas the rearward facing strobe is a single flashing unit. As a result you can identify whether the aircraft is coming towards you or away from you by the strobe flashes (double = towards you, single = away from you).

There is any consideration about the time? I'm trying to program a pic in order to simulate this effect in a model 1/144

This other discussion helps but you'll need to use a watch to time the sequence. There are plenty of videos on YouTube which are usable.

Thanks a lot mins! Yeah, I cron with my watch a video, but I was very frustrated calculating the 555 power supply so I ask :D If you want to answer my question I'll glad to mark it as accepted answer :)

No need to use a 555 if you have a uC, you can use one of the GPIO for the whole sequence :) My comments are not complete enough to make a good answer, someone may provide all the element and a reference from Airbus documentation. Good luck!

oh my god mins! Thanks a lot :D Well when I finished my circuit I'll post it :D

For the lights on the A340-200/-300 see Documentation page 129.
For the lights on the A340-500/-600 see Documentation page 133.
Use the following link to see the lighting regulations for commercial aircraft -  http://www.whelen.com/pb/Aviation/System%20Requirements/Anit-Collision%20Systems.pdf
Use of lights
AIM 4−3−23. Use of Aircraft Lights was updated in the latest edition.
Guidance about using aircraft lights during ground operations also appears in AC91-73B, “Part 91 and Part 135 Single-Pilot Procedures during Taxi Operations.”
h. Use of Exterior Aircraft Lights to Make Aircraft More Conspicuous.
(1) General. Exterior aircraft lights may be used to make an aircraft operating on the airport surface more conspicuous. Pilots may use various combinations of exterior lights to convey their location and intent to other pilots. Certain exterior lights may also be used in various combinations to signal whether the aircraft is on a taxiway or on a runway, in position on the runway but holding for takeoff clearance, crossing an active runway, or moving down the runway for takeoff.
NOTE: Because adherence to the guidelines in this AC are voluntary and aircraft equipment varies, pilots are cautioned not to rely solely on the status of an aircraft’s lights to determine the intentions of the pilot(s) of the other aircraft. Additionally, pilots must remember to comply with operating limitations on the aircraft’s lighting systems.
(2) Because adherence to the guidelines in this AC are voluntary and aircraft equipment varies, pilots are cautioned not to rely solely on the status of an aircraft’s lights to determine the intentions of the pilot(s) of the other aircraft. Additionally, pilots must remember to comply with operating limitations on the aircraft’s lighting systems.
(2) Exterior Lights. To the extent possible and consistent with aircraft equipage, operating limitations, and pilot procedures, pilots should illuminate exterior lights as follows:
(a) Engines Running. Turn on the rotating beacon whenever an engine is running.
(b) Taxiing. Prior to commencing taxi, turn on navigation, position, anti-collision, and logo lights, if available. To signal intent to other pilots, consider turning on the taxi light when the aircraft is moving or intending to move on the ground, and turning it off when stopped, yielding, or as a consideration to other pilots or ground personnel. Strobe lights should not be illuminated during taxi if they will adversely affect the vision of other pilots or ground personnel.
(c) Crossing a Runway. All exterior lights should be illuminated when crossing a runway.
CAUTION: Pilots should consider any adverse effects to safety that illuminating the forward facing lights will have on the vision of other pilots or ground personnel during runway crossings.
(d) Entering the Departure Runway for Takeoff or LUAW. When entering a runway after being cleared for takeoff, or when taxiing into position and hold, pilots should make their aircraft more conspicuous to aircraft on final behind them and to ATC by turning on lights (except landing lights) that highlight the aircraft’s silhouette. Strobe lights should not be illuminated if they will adversely affect the vision of other pilots.
(e) At Night, and When Cleared to LUAW. Consider lining up slightly (approximately 3 feet) to the left or right of the centerline (CL) to enable a landing aircraft to visually differentiate your aircraft from the runway lights.
(f) Takeoff. Landing lights should be turned on when takeoff clearance is received, or when commencing takeoff roll at an airport without an operating control tower.

thanks! that was I looking for, but links are forbidden or dead: The requested URL was rejected. Please consult with your administrator.


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How is the cockpit rear view of an Airbus A340?
Before anything I know this can be sound something stupid and obvious, but I swear I lost 3 or 4 hours searching images and videos before posting this question. So please be mercy with my poor knowledge.
I'm looking for a view of the rear side of the cockpit (when the door is, and the third and four ocuppant seat is).
I only get a very partial views, and the more detailed image is a diagram from the cockpit deck layout (the following is an example from A330, I could get the A340, but I'm not looking for a diagram):

Everyone knows the typical eye-lens shot of the panel, but it was impressive to me that get one of the rear view is really difficult, more even after the tragedy of the Germanian, where a lot of shots has no relevance with I'm looking for.
Any help will be preciated.
Thanks in advance.

I Googled for a340 360 cockpit view which returns, with others, this result

Thanks a lot Simon, this really help me. I could not make a picture by the 360º but it's perfect for me, because I'm modeling the cockpit in scale. Thanks a lot! Could you make your comment as answer so I accept it? I think really answer this.

@Simon You need to put that as an answer so that Leandro can mark it as an accepted answer. I was about to put that Airbus link as the answer but then saw your comment.

It seems far too easy and small to post as an answer but I have done so.  I'm pleased that it helped you.

@Simon It's not about pleasing me, but rather doing the right thing. You gave a perfectly fine and correct answer, it should be posted as an answer not as a comment, regardless how easy and small it appears. Comments are for comments, not for answers. Oh, and thanks for doing that. :)

I Googled for "a340 360 cockpit view" that returns, with others, this link.
The link is a 360-degree view of the A340 cockpit. Below is a frame grab for one of the angles:

the link does not work anymore


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Why is there a short tone in the ATC recording that cuts the pilot transmission using VOX?
I had an experience of listening to tower-to-pilot conversation and noticed that there was a short tone in the audio stream that suppresses the voice/audio signal and causes muting on the recording. I have a copy of the recording and the tone is around 100 Hz sawtooth wave. In the recording from the radio, it cuts the voice of the pilot while in the recording extracted from the module, there is this 100Hz sawtooth wave tone with around 0.5sec duration. Anyone has idea what might be causing this?

How were you "listening to tower-to-pilot conversation?" Where did the "recording" come from? Can we also have a copy? What is the "module" from which you say it was extracted? The more detail you can provide, the more likely you'll get a good answer.

There were two recordings, one from the operator module in the tower, and the other is from the radio interface board. The recording from the radio interface board has short muting on the pilot transmission, while the recording from the operator module in the tower includes the tone which causes the muting from the radio interface board recording.

Attached is a cut version of the transmission
during the tones in this recording, it signifies the muting on the other recording, just the same duration of the beep.
https://voca.ro/16rplfD4x9fc

@TypeIA , maybe you know something on this? I can't seem to find out where the tone comes from. One assumption is that it is from a coupled frequency, however, the reason for this tone is still unknown even if the tone is indeed coming from the coupled frequency.

Sorry, I don't. I can only say it doesn't sound like the normal heterodyne squeal that happens when two stations transmit simultaneously. I would follow up with the source of the data (facility or equipment manufacturer).

I see. Thanks for taking the time...unfortunately, i won't be able to provide with such details on the manufacturer and other details. Just that this uses frequency coupling, and the audio is improved if we de-couple it.

This one is also using analog radio... Could it be coming from the signaling? (i.e. squelch) -this is affecting various frequencies-

perhaps a notch filter might help ...but... :(

Could be a linear time code tone (LTC). I can't listen to the file, as it is no longer at the link provided, but time codes have been in use for clock synchronization for decades. the audio is probably being played back on a device not designed to handle the LTC track separately.


text:
What determines maximum speed of a propeller aircraft - Thrust or Power?
I'm reviewing training materials1 for straight and level flight.
The content focuses on drag types and explains that the required thrust curve is equivalent to the total drag curve. It then introduces the power required polar and states that velocity is related to available power.
Why not just say that thrust determines velocity?
What's the purpose of bringing in the power curve? Is it simply because Velocity = Power / Thrust?

1Page 17 under heading "POWER".
Also in an old printed manual from the CAA days. And also the Aviation Theory Centres flight training manual

Also, page 150 of the FAA's Aerodynamics for naval aviators mentions power and not thrust for a piston/prop. I'm feeling particularly dense when it comes to this concept for some reason. I can't seem to practically grasp why we must consider power when it is thrust equalling drag?

Interesting US Navy course: Thrust vs. Power

People, let's not confuse the newbie with endless comments, but write a proper answer!
Why power?
Power is reasonably constant over speed, so it is more useful than thrust when characterizing a propeller-driven airplane. The determination of thrust is much more complicated and error-prone. Power can be accurately measured on a test bench while only static thrust can be measured to an equal degree of accuracy (just tie the airplane to something really heavy and measure the force needed on those ropes). Thrust in flight (when it is really interesting) can only be approximated because so many factors will influence the measurement:

Propeller efficiency. This can vary a lot.
Airplane drag. What you  can measure is either fuel flow at a trimmed speed or acceleration at full throttle. Both will only give you an indication of the difference between thrust and drag, but not drag directly. Good drag estimation is a very laborious task!
Slipstream drag. Even if you know the drag of the airplane in flight to a reasonable degree, the change in flow speed and direction within the propeller slipstream will add another drag component which also needs to be determined in order to calculate thrust.

Why not just say that thrust determines velocity?

You are right, thrust (or, more precisely, the difference between thrust and drag) does determine velocity.

Good answer. Thrust dictates the physics. Power is a model of how thrust will behave at different airspeeds.

@JYZL -- no, it is equally valid to say that either thrust or power dictates the physics.  The book "Gossamer Odyssey" about MacCready's human-powered aircraft goes into great detail about the power output limitations of the human pilot-drove the aircraft design process -- we can compute the required power needed to fly an aircraft directly from the no-power sink rate at the airspeed of interest, and the aircraft weight-- I don't see how one can say that power does not drive the physics--

@quietflyer JYZL only agreed that thrust is the force in the equilibrium, not power. And that power limitations drive the design process of airplanes is hardly a novel insight.

@Crabsticks Thanks for posting the page number to the passage that is confusing you.
It is simply because the airplane has a power lever -- it does not have a thrust lever.  The propulsor (prop, fan, jet, whatever) generates thrust.  It also does work on the air at the rate (power) T*V.  In a helicopter (which is usually governed to constant speed), there can be a torque meter on the dash, so the flight manual there will be in terms of torque.
For all practical purposes, the terms thrust and power are interchangeable when we talk about how we fly an airplane.  When you increase thrust, we also increase power.
Piston propeller airplanes generally have a maximum power rating.  The shaft power the engine can deliver is pretty much independent of airspeed.  We have instruments that report RPM and manifold pressure (and sometimes torque).  So it makes sense to talk about operating the piston engine in terms of power.
Because the piston engine has a maximum power rating (maximum speed will occur at the engine's limits), a POH will talk about max speed occurring at max power.
The piston prop aircraft actually achieves maximum thrust at takeoff at sea level.  Feel how much it throws you back in your seat when you push the throttle forward on takeoff -- lots of static thrust.
So, if you imagine there was a 'thrust meter' on the panel, it would be all over the place during flight.  There is also no useful maximum allowable thrust that the pilot must watch -- like a maximum RPM, maximum manifold pressure, maximum exhaust temperature, etc.  The engine instruments are all about not breaking the engine.
Because of the way engines and propellers work, it makes more sense to operate a piston/prop in terms of power.

Just to add something to the other answers.

Why not just say that thrust determines velocity? What's the purpose of bringing in the power?

Using either thrust or power is really just a matter of ease of calculation.
An engine driving a propeller, delivers a power which is more or less constant with the speed. On the other hand, a jet engine delivers a thrust which is more or less constant with the speed.
So if you are analysing a propeller-driven airplane then it's easier to reason in terms of power, while if you are analysing a jet airplane then it's easier to reason in terms of thrust.
That's all.
Obviously you can always change from thrust to power and vice versa relying on the "definition" of power which is force*speed. So for example the power consumed by an airplane due to its aerodynamic drag $D$ flying at speed $V$ is $P_{drag}=D \times V$. The power consumed by a propeller creating a thrust $T$ with an efficiency $\eta$ at speed $V$ is $P_{prop}=\eta T \times V$.

Velocity is constant when Thrust = Drag

The purpose of any propulsion system is to produce thrust.

why talk of power with props?

This is a "left-over" from a time when early engineers, such as the Wright Brothers, put a propeller$^1$ on to any engine available to attempt flight.  Engines are rated in "horse power".

Power is Force × distance/time

With the aviation propeller application, the power of the engine is absorbed by the drag torque of the prop: drag force x the distance from the center of the prop shaft$^2$
This definition can lead to some very embarrassing observations because:

Thrust is a function of power and propeller efficiency

A 2000 Horsepower engine can be churning away without producing any thrust if the propeller efficiency is 0.
The full equation for propeller thrust is therefor:

Thrust is proportional to (Prop drag torque) × prop efficiency

Since "power required" = "prop drag torque" ("power" is directly translatable to "throttle setting"), the usage has stuck, often as RPMs or % Power, but this only refers to power into turning the prop.  Thrust output efficiency will vary with speed, especially for fixed pitch props.

variable pitch props have a far greater speed range of efficient thrust output until...

Pitch to maintin optimal prop AoA to the relative wind
becomes too great

Incoming air velocity into the prop disk gets closer and
closer to the exit velocity

This is why prop driven planes max out at around 400 knots, even with huge power plants and variable pitch props.

so how do you know how much thrust a propeller is producing?

By calculating the angle of dive in a glide for a given airspeed and multiplying the sine of this angle × the airplane weight.
This is now the thrust force required for level flight (for that particular aircraft).
If you want to know your thrust at full power and a lower airspeed, add sine angle of climb to your value.
Doing this, and plotting data points, can give some very good thrust data for a given aircraft/engine/prop combination.

and, of course, one can try various props for climbing or cruising needs.

$^1$ it should be noted that the Wright Brothers did make considerable progress in improving propeller efficiency.
$^2$ this can be 1:1 with engine crankshaft or it can be geared

Power is what you put in.
Thrust is what you get out.
The opposed aerodynamic drag is what's left over onve you have got the power from the engine and into the air.
Engines are designed to provide a power curve.
Torque is proportional to Power per engine RPM - so you could if you wish deal with either, but power makes most practical sense.
An engine usually has an optimum RPM point, fuel supply, aspiration, air inlet and engine temperature and more. This leads into gearboxes and variable speed propellors and ... .
From there you go to how the power is converted to oppose the power generated by aerodynamic (and other) forces.
A propellor has it's own power vs RPM curve - and will have optimum conditions - air density, pitch, profile, ... .
The aircraft generates drag (and lift which is best stayed away from at this level :-) ). This will be frontal, generated by laminar flow & vortices at various places and ... .
Between power in and thrust there tends to be a lot of " ... " :-).
Overall the engines produces power which is used to develop the aerodynamic power required to overcome the drag forces (and ... :-) ).
A jet engine is more suited to being described by thrust as it is more fundamental to the description of the systems operation - whether pure jet / ducted / high-low bypass / ( ...) the engine tends to be more likely to be considered as a unit that generates thrust. (I've often seen thrust figues for jets but power figures are less commonly used.) Power for a jet is somewhat meaningless for a jet except at specified velocity.
Power = force x distance / time. Without the time component a jet delivers no power.
An eg Saturn V Moon rocket, at the point of launch is developing maximum thrust BUT zero power as it is not moving. But not for long. Zero power at takeoff is true for all stationary vehicles - including rockets, Tesla's and Usain Bolt.


text:
Does the useful load contain taxi fuel?
While doing the “Mass and Balance” subject for the EASA ATPL, I came around two useful load definitions which contradict itself.
The first definition says:

The Useful Load is the total mass of the passengers, baggage and cargo, including any non-revenue load and usable fuel.

By saying usable fuel I assume that it includes taxi fuel + takeoff fuel, but then in the other definition they say about the All Up Mass (AUM):

The AUM in the diagram above refers to the mass of the aircraft at Take-Off because the Useful Load is always determined with reference to the aircraft mass with Take-Off Fuel on board.

Here’s the diagram for reference:

Which one is correct?
If you could give me official sources for it I would appreciate :)

Yes, the useful load includes taxi fuel.
Both definitions are correct and do not contradict each other:

The Useful Load is the total mass of the passengers, baggage and cargo, including any non-revenue load and usable fuel.

This statement is true.  Think of useful load as anything that’s not part of the actual aircraft.  You specifically mentioned taxi fuel and takeoff fuel, which are both usable fuel and included, but then added a second quote:

The AUM in the diagram above refers to the mass of the aircraft at Take-Off because the Useful Load is always determined with reference to the aircraft mass with Take-Off Fuel on board.

Your question insinuates that there is a contradiction between the two because the second definition excludes taxi fuel.
While it is true that the second definition includes takeoff fuel only, it is not because the definition of useful load is any different, it is simply because once you are at the hold short and ready for takeoff any fuel you planned to use for taxi has already been burned!

Thank you, it does make sense now :) Are there any official source, like from ICAO or EASA, where they specifically say that?

Where they specifically say what?  That you use up taxi fuel when you taxi?  You can't takeoff with taxi fuel because by definition you are no longer taxiing.  Fuel is fuel at that point, it isn't stored in separate tanks...  (don't overthink this!)

You’re right, I tend to overthink sometimes… I just wanted an official source from that definition “useful load”

Where did that first definition come from? Because it says all usable fuel is included. That covers all fuel except UNusable fuel.

From Mass and Balance Padpilot book


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What is the worlds shortest runway for FAR 23 commuter type aircraft?
This article lists the airport at Saba as the worlds shortest runway at 1300 ft. The runway is built on a bit of flat land on the side of the volcano that makes up the island. Nowadays STOL aircraft land here, previously the aircraft had to come in skimming over the wave tops and zoom climb onto the runway.
The Twin Otter can land here. Does Saba really have the shortest runway on earth for FAR 23 commuter type aircraft, or are there any shorter ones?


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Why is *vertical* autorotation in a helicopter not recommended?
Helicopters can autorotate back to earth in case of emergency. The FAA recommends a flight profile similar to the following procedure:

Notice that in section (2) there is forward speed: vertical autorotation is not recommended. Why is that?

Well, the reference frame for lift in a helicopter is the inflow velocity at the blades, not the downward speed of the fuselage. So it is actual lift that is generated.

Of course it is... Autorotation is an special case of windmilling where the rotor distributes lift and drag so that the energy transferred from the airstream to the rotor maximizes the thrust for any descent speed...

If you have no forward momentum to play with then you have no margin for error.  If your descent rate gets too high while you are low to the ground then there is nothing you can do but fall.  At least if you have some forward motion you can flare to trade some of that momentum for lift.

Even quadcopter pilots are cautioned against this. Descending straight down puts you in your own vortex ring and you could lose lift or lose control.

Isn't a lost-power helicopter a lot like an autogiro?

Yes it is - like an autogiro without engine oower.

Maybe the FAA also just assumes that you WANT to move the 'copter to an optimal landing spot? The likelihood that "straight down" is the most ideal place seems very low. "Don't try to improve your location over land" doesn't seem like anything they'd care to recommend. Also the flare at step 3 can't work/happen if there's no forward motion.

Why is vertical gliding in a fixed-wing aircraft not recommended? The answers are not entirely unrelated.

@reirab it might be surviveable in a helicopter though.

Apart from the physics/aerodynamics of airflow and energy management, what about the practicality of seeing where you are going? If descending vertically, your touchdown point is under your seat. Even with windows in the forward floor, there is still a blind spot directly underneath, isn't there? If you are moving forward you can see where you will touch down, at least until the flare; at that point you would be close enough to the ground that a view directly below isn't necessary, no?

When the engine fails in a single engine helicopter it can autorotate back to earth: it gives up potential energy from reducing height to keep the rotor turning, which then continues to provide lift. Autorotation can  take place straight downwards in vertical flight, but the general recommendation is to maintain forward speed, like a fixed wing gliding: the rate of descent is much lower if there is forward speed.
 Image source
We associate helicopters with hovering, but this is a strenuous effort. Even a bit of forward velocity generates translational lift, which makes it much easier for the rotor to generate lift:

The forward inflow tilts the lift vector forward, decreasing induced drag and blade torque, and increasing lift. Or stated in a different way: the airstream is flowing in already, and does not need to be accelerated from zero. The rotor now starts to work more like a fixed wing does.
The airstream through the rotor experiences less interference from the fuselage.

The effect of forward velocity on auto rotational rate of descent is depicted in a graph in this book:

Going back to vertical autorotation: the vertical upward airstream needs to go through the rotor fast enough to reach the windmilling state, so that lift is created by decelerating the air passing through it. If we compute the lift component per area of a vertically autorotating rotor, it is comparable to a $C_D$ value of 1.1 to 1.2 referenced to the rotor area. According to this source:

a flat plate has a $C_D$ of 1.28
a parachute has a $C_D$ of 1.4.

So in vertical descent, the auto-rotating rotor is almost as good as a parachute of the same area - it’s just that the parachute size is a bit small for the typical payload of a helicopter, resulting in vertical descent speeds of between 3,600 to 6,200 ft/min. By way of comparison:

Air France 447 fell to the ground with a vertical descent rate of 10,000 ft/min.
Captain Sullenberger's plane took four minutes to reach the Hudson in a proper glide, from 2,060 ft altitude = average of 500 ft/min.

Two factors make autorotation much more survivable though:

The descent rate can be “flared” by pulling the cyclic back (exchanging forward velocity for more rotor kinetic energy) and then collective up just before ground contact, slowing down the rotor and increasing lift. The pilot only has one shot at this.
The descent rate is a lot less if autorotation is done at a forward speed,   the best one being the optimum climb speed.

Note that in a vertical descend there is no pullback of the cyclic, only increase of collective - plus the rate of descent is higher. A higher speed and fewer means to brake, that is not recommended!
A side note
The windmilling rotor does not turn the other way! The incoming air from underneath tilts the lift vector forward, like in a glider. Part of the rotor disk is driven by the aeroforces into the same direction as it was when still under power.
 Image source

Nice answer, but I can't help disliking that graph.  Due to the way it displays its axis, it appears to show the first quadrant but instead shows the second, so appears to show that the vertical velocity is higher when moving.  Could be fixed by using positive values for descent, or just labelling the x axis at the top (y=0).  Not to take anything away from this answer, it's just unfortunate.

I think the keyword translational lift should be mentioned regarding the shape of that descent rate graph.

The point in 1. factor is that the kinetic energy due to forward motion is available for generating the lift to arrest the descent in addition to the (very little, unfortunately) energy stored in the rotor itself.

Forgetting THEORY... a vertical autorotation IS possible and can be accomplished safely. To answer this question put to me by my Co-pilot that day in Vietnam, I took our H-Model Huey up to 5,000' and confirmed hover. I lowered the collective and chopped the throttle to split the needles and monitored rotor RPM to ensure no over-speed while keeping the cyclic centered for true vertical. I used collective to stabilize our sink rate. Once satisfied that the maneuver was safe, I recovered at about 1,000' by pushing the cyclic forward and recovering power.
We experienced no issues with vortex ring theory or any indication that this maneuver was dangerous. Had I needed to actually put it down, I would have initiated a forward cyclic aspect in order to perform a standard flare and set-down once below that 1,000' I chose. In Army flight school in the 1960's, we practiced every possible aspect of auto-rotations ALWAYS to the ground with NO power recovery at 50' nonsense. I personally believe it's irresponsible and insane to not train a helicopter pilot for full ground contact autos. What? Is God going to suddenly show up and help in that last 50' or so?
SIMS are NOT an acceptable substitute for actual practice. We did hovering autos, run-on autos, 180° and 360° autos, full-speed deceleration autos, but my all-time favorite was called "Spot Autos." The IP picked a spot on the runway - usually one of the numbers and I initiated an auto from pattern altitude and speed on the runway heading noting my steep glide angle through the chin bubble.
Keeping collective down and using only cyclic, I flared the chopper to an almost dead stop - closely monitoring rotor rpm and pulling collective when needed to prevent over-speed. Cyclic was pushed forward to start the wonderfully fast descent again - oh wee - we could get at least two and sometimes three flares on the way down - the last one was to a stop right on the number chosen and pull what was in essence a hovering auto to land.
We always completed all our autos to the ground with all of these maneuvers and they were truly FUN to do! Our IP's defined expertise and competence and did an excellent job of instilling those same characteristics into all of us, knowing that where we were headed we would need every training advantage we could handle. My two cents (1,955 combat helicopter flight hours in Vietnam slicks and guns).

Thanks for sharing this, experience from the real world. A highly trained helicopter pilot like yourself would be able to land the ship in almost any situation, but would the FAA recommend anything else than the safest option?

Would weight be a factor? I assume you didn't have a Huey full of troops when you performed that maneuver.

Just want to comment that vertical autorotation, transitioning to forwards flight before flare and landing is total a normal skill learned flight training and can be used for range variation. if the FAA banned it it must be an American thing. More weight just makes everything faster, giving you less time.

There are three good reasons to avoid Vertical Autorotation.
First, Vertical Autorotation is way more likely to lead to a Vortex Ring condition where the air exiting the rotor disk gets recirculated back through the rotor disk.  The recirculated air in the Vortex Ring then limits the amount of airflow/energy available for conversion to Rotor Disk rotational velocity which is critical to successfully completing that part of the Auto Rotation maneuver essential to survival (the flare up to touchdown).
Second, the forward velocity increases the amount of energy available for conversion to rotor disk speed.
Third, forward velocity allows landing shock to be shared between different harnesses and seat shock absorbers thus decreasing the load on any particular axis.

A simple way to understand the problem is this: To get lift, the rotor has to push air down. So there will be descending air just below the rotor. If you descend straight down, you're staying with that descending air, and it will carry you down with it. Flying forward gets you out of the descending air the rotor created so it can't push down on you as much.

I don't think it's physically possible to enter a VRS in autorotation

Here. I found a source for that: It is not possible to enter the vortex ring state whilst the helicopter is in autorotation. https://www.skybrary.aero/index.php/Vortex_Ring

@TomMcW: Even though air is moving upward through the rotors during auto-rotation, the helicopter is still going to be disturbing the air underneath it.  Efficient lift generation requires entering undisturbed air.

@supercat I'm not saying it's best to go straight down. Translational motion makes rotors more efficient in all situations. I'm just saying a vrs is not possible in ar.

My reasoning might be flawed, but the upward moving air toward the center of the disc is the very thing creating the rotation. If you increase pitch enough to create a significant downwash then the rotors will slow. AFAIK, vrs occurs when attempting to hover right at the performance limits, therefore at a high aoa.

@DavidSchwartz To be in a pure windmilling state, the helicopter has to descend downwards with quite a high velocity. Obviously that is not desired - VRS is the region between hover and windmilling, and in order to reduce the rate of descent as much as possible the pilot will stay as close as he can to the VRS region. There is usually a little induced down flow through portions of the rotor disk, although most of the flow will be upwards. ref

@Koyovis Any lift the helicopter is getting comes from pushing air down. If that lift is coming from the rotors, then the rotors are pushing air down. The helicopter will be embedded in a block of downward moving air, carrying it down with the air.

@DavidSchwartz If the air flows through the rotor fast enough, the lift is obtained by decelerating the air - outflow is in the same direction as inflow.

@Koyovis: To create lift, the rotor must create a pressure differential between the air above and the air below.  If the pressure of the air immediately below the rotor is greater than the pressure of air below that, such difference will cause the air below the rotor to accelerate downward.  Can an unpowered rotor reduce the pressure of air above without increasing the pressure of air below?

You have to consider the power required by the helicopter in flight, represented by the red curve in the graph.

The blue line is the power provided by the rotor in autorotation. As you can see at zero airspeed the power requiered is much bigger than at 50, 60 or 70 kts. Therefore, you power deficit will be also much bigger at zero airspeed, resulting in an increased rate of descent.
Another advantage given by speed is the ability to flare (steps 3-4 in the flight profile recommended by FAA). During the flare you use the kinetic energy provided by forward speed to reduce your descent. With zero airspeed you completely lose this posibility, the only chance of reducing rate of descent remaining will be increasing the collective (and most likely it will not be enough to prevent a very hard landing).
A third reason would be that for the pilot it's easier to judge height above the ground if there is some forward speed, and also the helicopter is more stable directionally.
Bottom line, the preferred airspeed range for autorotation is the one shaded green in the graph, between minimum-power-speed and best-range-speed. There are situations where the yellow range is used (confined area, some procedures for night autorotation), but this area doesn't extend below 30 kts, anyway.

Wonderfully illustrative graph.

During autorotation, forward speed is used to control rotor head speed. In auto, the engine is disconnected (in the case of tail rotor failure) or just plain dead, so it can't be used to control rotor speed.
In a vertical descent, the rotor head will eventually overspeed from the air rushing past the blades, and the rotor blades will depart from the aircraft. Not good.
The air hitting the blades from forward flight is used to induce drag on the rotor blades, slowing them down. The faster the helicopter moves forward, the greater the drag.
So the pilot, in auto, uses forward airspeed to control rotor speed. If the rotor head speed builds up too much, nose down a bit to gain airspeed and slow the rotor down. If the rotor head starts slowing down, then back off the forward velocity to let the rotor head pick up speed.
Forward flight also aids in maneuvering the helicopter when choosing a touchdown point, but mainly, it is used to keep the rotor speed in the green.
Every helicopter has an ideal autorotation forward flight velocity, that should keep rotor head speed in the green. In a Bell JetRanger, it's around 60 kts I believe, though this is a general guideline, not an absolute.
Theoretically, one could increase blade pitch to an overspending head to slow it down, but forward flight is a more precise way of doing this, and avoids the risk of inadvertently slowing the head down too much.

In your last paragraph you say that in a vertical autorotation the rotor can be prevented from overspeeding - pull the collective up far enough and the blades will stall. Again something that it is much harder to do without any horizontal speed. And the descend speed remains frighteningly high even with the rotor at 100%.

Rotor rpm control is by collective. No vortex ring in autorotation..since Air is flowing in wrong direction. Vertical autorotation  is possible but risky since limited excess energy, greater energy with airspeed ,so you have more energy for the flare, allows margins for errors during flares.  and you can pick your landing  area fly to it and obviously see it in advance ..

There are many wrong answers in this thread but I want to address one that any rated helicopter pilot should be able to answer (which judging by the answers in this thread may be not as true as I’m hoping) and that is:
YOU CANNOT GET VORTEX RING STATE IN AN AUTOROTATION
The three things you need for VRS or “Settling with Power” (FAA definition) are:

Rate of descent greater than 300fpm
Speed less than ETL
POWER APPLIED

Obviously if the engine has quit you cannot have power applied.
That being said, you do still have energy stored in the helicopter in the form of potential energy (in altitude above ground level) and kinetic energy (in the helicopters airspeed). Kinetic energy increases exponentially with airspeed i.e. if you double your airspeed (ex. 30 to 60 kts) you triple the amount of kinetic energy you can use to maintain your rotor RPM in the flare (that you will need a lot of to arrest the rate of descent and forward airspeed prior to touching down)
If you have no airspeed you have a higher rate of descent in the auto and less energy to arrest that rate of descent with prior to landing.
Answers to these questions and more can be found in the Helicopter Flying Handbook which is free to download from the FAA website!
-FAA RW Commercial Pilot and CFI-I

Kinetic energy increases quadratically with speed, not exponentially. If you double the speed, you have quadrupled the kinetic energy. Specifically, kinetic energy = 1/2 m * v^2.


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How can I transfer my US License to the UK?
I'm thinking of moving over to the UK to fly for British Airways since they only ask for 500 hours Pilot-in-Command time to become a First Officer.
I currently hold a CPL and am Instrument Rated. I was wondering what the process was to transfer my FAA license to a UK one.

Your best bet is to contact British Airways and ask them. If they want you, they will tell you how to do that.

You will need to follow the "route 1" conversion requirements listed here before applying to the airline:
https://www.caa.co.uk/commercial-industry/pilot-licences/non-uk-licences/third-country-cpl-and-atpl-licence-conversion-requirements-from-1-january-2023/
Essentially it will involve sitting the ATPL theory exams (with a 650 hour theory course, unless you've already got ATPL theory credit on your license), some practical flight training before a skills test.
The validation pathway is not for you as that expires after one year.
Of course you should not begin to think about this process unless you already have the unrestricted right to work in the UK. That is a criteria on the BA website, suggesting they cannot sponsor you for a working visa.

The details of validating an ICAO-compliant licence for work in the UK is detailed on the CAA website
https://www.caa.co.uk/commercial-industry/pilot-licences/non-uk-licences/validating-an-icao-licence-for-work/

Validating an ICAO licence for work allows you to fly for remuneration on non-commercial operations, commercial air transport or other commercial activities using your ICAO licence.

There are basically the requirements you probably expect; medical validity, proficiency check, and of course a fee! Most of this will probably be arranged by your new employer.